What is this below the automatic air vent valve?

[fullel]

The (apparently rotated) picture shows my badly scaled up automatic airvent valve just a few cm downstream from the pump. I have some water hammer (hydraulic shock) when the pump goes off and this scaled up air vent is my prime suspect. I am ready to drain the system down and screw this old vent off. By the look of the amount of nipple, I will have to cut the olive off, clean the pipe and replace with the new compression 15mm auto air vent.

What I don't know is what the object is immediately below the air vent sticking out to the left and whether I need to replace that too. Is it a manual bleed valve for example?

Thanks.

 

[jtsplumbing]

Left over from old system, probably solid fuel BB, what boiler do you have now ? if you have a pressurised system you will have a more up-to-date PRV, so you can cut out and remove this old fitting

 

[fullel]

Fullel,

Where is your 6 bar coming from, surly not domestic.....

The tall auto air vent at the top is 6 bar, isn't it? There was also one attached to the primary return from the HW cylinder which was weeping and replaced.

 

[Dotty]

No no no no no.....

That means it can be used on systems with pressure up to 6 bar.

 

[fullel]

Ah yes. Well, still don't know why there are two. So, just replacing the top one should work then? I kind of thought the water hammer was caused by air not being able get _in_ to fill the 'vaccuum' when the pump stops.

 

[Dotty]

The top one is an Auto Air Vent. It vents air out of the system automatically (see what I did there?) but doesn't. or shouldn't, allow air back in.

The bottom one is a Pressure Relief, or Safety, valve. It automatically releases pressure over a given point which, in your case, is 3 bar.

Neither the failure, nor the operation, of either component would result in the noise you say you have.

I'd suspect a sticky flapper type none return valve to be honest.

They have two completely different yet vital functions

 

[fullel]

Right, I'll leave them alone then.

 

[happyflyer]

Hells Bells!!! :sweatdrop: I think they are going to make Plumbing a trade next week